user namespace: usb: make usb urbs user namespace aware (v2)

Add to the dev_state and alloc_async structures the user namespace
corresponding to the uid and euid.  Pass these to kill_pid_info_as_uid(),
which can then implement a proper, user-namespace-aware uid check.

Changelog:
Sep 20: Per Oleg's suggestion: Instead of caching and passing user namespace,
	uid, and euid each separately, pass a struct cred.
Sep 26: Address Alan Stern's comments: don't define a struct cred at
	usbdev_open(), and take and put a cred at async_completed() to
	ensure it lasts for the duration of kill_pid_info_as_cred().

Signed-off-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 16 insertions, 8 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 291c9700be75..d252be2d3de5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1344,13 +1344,24 @@ int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
         return error;
 }
 
+static int kill_as_cred_perm(const struct cred *cred,
+                             struct task_struct *target)
+{
+        const struct cred *pcred = __task_cred(target);
+        if (cred->user_ns != pcred->user_ns)
+                return 0;
+        if (cred->euid != pcred->suid && cred->euid != pcred->uid &&
+            cred->uid  != pcred->suid && cred->uid  != pcred->uid)
+                return 0;
+        return 1;
+}
+
 /* like kill_pid_info(), but doesn't use uid/euid of "current" */
-int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
-                      uid_t uid, uid_t euid, u32 secid)
+int kill_pid_info_as_cred(int sig, struct siginfo *info, struct pid *pid,
+                         const struct cred *cred, u32 secid)
 {
         int ret = -EINVAL;
         struct task_struct *p;
-        const struct cred *pcred;
         unsigned long flags;
 
         if (!valid_signal(sig))
@@ -1362,10 +1373,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
                 ret = -ESRCH;
                 goto out_unlock;
         }
-        pcred = __task_cred(p);
-        if (si_fromuser(info) &&
-            euid != pcred->suid && euid != pcred->uid &&
-            uid  != pcred->suid && uid  != pcred->uid) {
+        if (si_fromuser(info) && !kill_as_cred_perm(cred, p)) {
                 ret = -EPERM;
                 goto out_unlock;
         }
@@ -1384,7 +1392,7 @@ out_unlock:
         rcu_read_unlock();
         return ret;
 }
-EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);
+EXPORT_SYMBOL_GPL(kill_pid_info_as_cred);
 
 /*
  * kill_something_info() interprets pid in interesting ways just like kill(2).